Spectral analysis of living tissue can be used to detect various forms of cancer and other types of diseases. In spectral analysis, light illuminates tissue region under examination and a light detector detects optical properties of the illuminated tissue region by measuring light energy modified by its interaction with the tissue region in a pre-determined frequency and amplitude domain. Optical properties include absorption, luminescence, fluorescence, frequency and time-domain responses to various materials injected to the tissue region and other electromagnetic responses. Diseased tissue may be identified by comparing a spectrum obtained to spectra of normal tissue obtained under the same controlled conditions.
Current devices available for tissue characterization using spectral analysis include night vision sensing systems with filtering adapted to be used with endoscopes and multichannel fiber optic delivery systems. The latter systems typically include a light source, an optical conduit, a light applicator and receiver, a second light conduit, a spectrometer and a display unit. These systems tend to be very expensive, to require large accompanying electronic systems, and to be complex requiring operator training.
The optical fibers used as optical conduits in the multichannel fiber optic delivery systems are source of design difficulties. In order to transport an adequate amount of light energy from the light source to a tissue region inside a body, a significant amount of optical fibers must be included in an interventional device. An interventional device, such as a catheter, however, does not include a lot of space and higher quality optical fibers, which take up less space, are expensive.
Optical fibers also lack mechanical properties necessary to be used with an interventional device. Optical fibers can break when flexed and have a relatively high stiffness compared to conventional catheter materials. Therefore, it is difficult to design a flexible tip for a catheter, which includes optical fibers and overall flexibility of an interventional device which include optical fibers is limited.
Furthermore, optical fibers require an expensive terminating connector and must be properly coupled to afford adequate light throughput. Signal efficiency of fiber based devices depends greatly upon the devices' ability to couple sufficient light into the fibers at the desired wavelength. For spectral analysis, filtered broadband light sources are preferred over laser light sources for cost and frequency versatility. However, it is a challenge to efficiently couple light from a lamp source into fibers with small diameters. Although laser light is more easily coupled into optical fibers, laser light sources are generally more expensive, are obtainable in only a few selected wavelengths, and are subject to more critical regulatory controls than other light sources. Furthermore, light emitted by the subject illuminated by a laser light tends to be weak and is also subject to all of the loss mechanisms and inefficiencies problematical to a laser system.
Additional hardware, such as connectors and couplers, and the need to provide one or more optical conduits along the length of the interventional device, make conventional devices used for spectral analysis relatively expensive, inconvenient, and perhaps impractical.